Movie projectors—at least those that use film—are very complex devices. They have to run the film at a continuous speed, manage the light that shines through the film, and read an optical sound track. It's not easy.

In this video, Bill Hammack (also known as The Engineer Guy) explains the intricate mechanics of the film projector. If you like to geek out over impressive machinery, here's your chance.

Note: Today, lots of movies are projected digitally. While some of the core technical challenges remain—like keeping sound and picture in sync—many of the solutions are completely different.